Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine that generates a mechanical power output. In order to maximize the power output generated by this combustion process, the engine is often equipped with a divided exhaust manifold in fluid communication with a turbocharged air induction system.
The divided exhaust manifold increases engine power by helping to preserve exhaust pulse energy generated by the engine's combustion chambers. Preserving the exhaust pulse energy improves the turbocharger's operation, which results in a more efficient use of fuel. In addition, the turbocharged air induction system increases engine power by forcing more air into the combustion chambers than would otherwise be possible. This increased amount of air allows for enhanced fueling that further increases the power output generated by the engine.
However, during use and due to high operating temperatures, components of the turbocharger wear down and need to be replaced. Some of these components can include attachment flanges on the turbochargers, which can be damaged during use and thus, they need to be replaced or remanufactured. Coating systems with acceptable oxidation resistance (e.g. Fe-22Cr-6Al) are readily available and are effective to applications of around 600° C. However, at higher temperatures, such as 800° C. and during thermal cycling, components such as attachment flanges have failed due to separation of the Fe-22Cr-6Al coating at the substrate or component surface. The separation occurs due to oxidation of the base material side of the substrate-coating interface surface and during thermal cycling, as the poorly adhered oxide on the cast iron turbocharger's surface tends to spall, leading to separation of the thermal spray coating. During the thermal spray coating process, the coatings are not completely dense, and the opportunity for air or gas to seep into the coating exists and difficult to eliminate. Even using a thermal spray coating with higher oxidation resistance will not necessarily work because the same propensity for oxidation of the cast iron surface at the coating surface still exists.
U.S. Patent Publication No. 2012/030873 discloses a that to manufacture a thermal barrier coating structure on a substrate surface, a working chamber having a plasma torch is provided, a plasma jet is generated in that a plasma gas is conducted through the plasma torch and is heated therein by means of electric gas discharge, electromagnetic induction or microwaves, and the plasma jet is directed to the surface of a substrate introduced into the working chamber. To manufacture the thermal barrier coating, a voltage is additionally applied between the plasma torch and the substrate to generate an arc between the plasma torch and the substrate and the substrate surface is cleaned by means of the light arc, wherein the substrate remains in the working chamber after the arc cleaning and an oxide layer is generated on the cleaned substrate surface and a thermal barrier coating is applied by means of a plasma spray process. However, this process still does not reduce or eliminate the potential separation of the coating structure due to oxidation at the surface of the substrate.
Thus, there is a need for an improved process that reduces or prevents oxidation of the substrate surface and allows the components such as attachment flanges of turbochargers to be remanufactured.